The thalamic reticular nucleus (TRN) is a thin layer of GABAergic neurons surrounding the thalamus. Due to its strategic location, TRN is suggested to be involved in the regulation of thalamic cortical communication and thus the cognitive process of sensor filtering. The issue is how. We will take advantage of the simplicity of the in vitro somatosensory thalamocortical slice preparation, which preserves intact pathway between the thalamus and cortex, to dissect the neuronal circuit involving TRN. We will apply the novel technique of laser-scanning photostimulation, in which a focused UV laser is used to release caged glutamate in a small region to specifically stimulate the soma and dendrites; this also has the advantage of not activating fibers of passage. We will look at two aspects of TRN function. First, we will prove that TRN is involved in the "egocentric" cortical regulation of thalamic information relay. Second, we will show that higher order thalamic relays, unlike the first order relays, receive diffused TRN inputs that enable them to function as integrators of sensory information. The thalamus is an important brain structure that serves as the gateway of sensory information to the cerebral cortex. Epilepsy has been known to be related to abnormal activities in the thalamus and many disorders, such as stroke, that damage the thalamus in some cases cause poorly understood clinical phenomena, e.g. thalamic pain. The research in this proposal will help understand the basic thalamic circuitry and eventually contribute to treatment of these conditions. [unreadable] [unreadable] [unreadable]